1. Field of the Invention
This invention relates to photosensor apparatus.
2. Description of the Prior Art
This photosensor is used for such purposes as detecting the focal position by detecting optical image data in a camera, a video camera, etc. with a plurality of light-receiving elements arranged on the image focusing plane of an image focusing optical system.
In the case of the focal position detection or the like, the brightness of an optical image varies over a wide range and also varies with time. Therefore, it is necessary to always vary the light sensitivity to a suitable level and hold optical image data at a certain instant. Since the light sensitivity of the light receiving element is constant, the adjustment of the light sensitivity is done by storing photons produced in the light-receiving elements and controlling the storage time with the storage value as the output signal. To adjust the storage time, the value of stored photons must always be monitored. However, where a large number of light-receiving elements are used, it is difficult to monitor all the stored values. Accordingly, it has been in practice to monitor the average value of the stored value. However, since the average value is monitored, the output of the light-receiving elements on which light of high illumination intensity is incident is liable to exceed the measurement range. In such a case, it is impossible to determine the extent, to which the measurement range is surpassed.
In order to avoid this, it is thought to progressively scan all or suitably selected ones of the light-receiving elements in which light integration is simultaneously done, thereby monitoring the output of the light-receiving elements. However, there is a limitation on the scanning speed. Therefore, a deviation of the instant of detection of the light-receiving element output occurs, so that in case where the illumination intensity of the optical image varies in a short period of time, the output is liable to exceed a constant range before the completion of one scanning period. In such a case, it is difficult to set the proper light integration period.